How did Germany's invasion of Poland turn a European crisis into world war?

Correct answer: Britain and France declared war against Germany

The direct answer is A: Britain and France declared war on Germany. Germany invaded Poland on 1 September 1939. Britain and France had promised to support Poland, so after the invasion they declared war on Germany on 3 September 1939. Step by step: Germany attacked Poland; the attack violated the European security arrangement and the promise made to Poland; Britain and France responded with declarations of war; the conflict therefore expanded beyond a local European attack and became the beginning of the Second World War in Europe. Option A is correct because those declarations brought two major powers directly into the conflict. Option B is wrong because Japan did not immediately surrender and later fought the Allies. Option C is wrong because the United Nations did not yet exist and did not attack Germany. Option D is wrong because Russia did not free France in response to the invasion. Memory cue: Poland, 1939, Britain and France, World War II.